As to the Oct. 9 as the Hangul Day in Korea: King Sejong the Great created
Hangul in 1443 and proclaimed somewhere around that time. When Hangul
scholars of Korea studied Hangul and moved for the national holiday in
celebration of Hangul invention, they calculated back the approximate date
according to the data they could come by, and they finally determined
"Oct. 9" as the closest day to the proclamation of Hangul. (As for more
precise data, I'm going to ask to some of Korean linguists in Korea.) At that
time, I mean, during King Sejong's rule, we Korea used the lunar calendar.
So in fact, the exact date should differ accordingly each year. But the
Korean government at the time of Hangul Day determination gave very much
(official) emphasis onto Western calendar at the expense of even some of
important traditional holidays such as New Years Day in lunar calendar!
Yet, they were better than the current government which excluded Hangul Day
from national holidays!
Sungjin HAN
Program in Computational Linguistics
Department of Philosophy
Carnegie Mellon University

Hangul Day (pronounced as "han-gul-nal" in Hangul) is always on
Oct. 9th by the Gregorian calendar. Like Dr. Schaufele, I doubt that
Koreans have been observing the Gregorian calendar since the 15th century,
but since Korea opened its door to the western world around the end of 19th
century, it adopted most of the western standards including metric system
and the calendar system.
As a Korean computational linguist, I am obviously very excited
about Martin Haspelmath's proposal to recognize Hangul Day as the World
Linguistics Day. If I get more information about the Hangul Day, I will
make another post here.
--
Jong-Gyun Lim 212) 939-7113 704 Schapiro Building
Department of Computer Science Columbia University